Control of brown rot and blue mold of peach and nectarine by short hot water brushing and yeast antagonists

Abstract

We examined the possible use of a hot water brushing (HWB) treatment to disinfect nectarine and peach fruit. In vitro studies showed Monilinia fructicola to be more sensitive than Penicillium expansum to high temperature. In vivo studies of inoculation of peach and nectarine fruit with M. fructicola followed by HWB at 55 or 60 degreesC for 20 s gave 70 and 80% decay inhibition, respectively, compared with the control. The inhibition percentage of M. fructicola with HWB were similar, if HWB was applied shortly after inoculation or 24 h later. In contrast, the sensitivity of P. expansum spores inoculated into wounds increased when the fruit were treated with HWB 24 h after the inoculation, compared with treatment just after inoculation. The combination of HWB with the application of yeast antagonists was also investigated. We found that treating fruit with HWB at 60 C for 20 s and then dipping them into a cell suspension (10(8) cells per ml) of Candida spp. 24 h after inoculation with P. expansum reduced decay development by 60% compared with the controls. Another yeast antagonist, Candida oleophila was inferior in its ability to control Penicillium expansum and M. fructicola compared with other Candida spp. The combination of HWB and Candida spp. showed no significant additional effect against M. fructicola, compared with HWB alone. HWB alone, at 60 C for 20 s, reduced brown rot development to very low rates. In storage experiments covering 30 days at 0 C and 10 days of shelf life, HWB and Candida spp. applied separately were each able to reduce natural decay incidence to commercially acceptable levels ( < 5%), and combining them showed no additional effect. SEM analysis showed a direct effect of HWB mainly on M. fructicola. The HWB treatment did not cause surface damage to the fruit or impair quality.